A domain controller is a server computer system that maintains user accounts associated with one or more client computer systems. The domain controller, together with the client computer systems associated with it, is known as a domain. A domain may also have multiple domain controllers. When a user has an account on a domain controller, the user can log on to any client computer system within the domain, and the user account is authenticated through the domain controller.
To reduce the need for maintaining duplicate user accounts throughout an organization (e.g., when a user is authorized to access client computer systems in multiple domains), a trust may be established between two or more domains. In this scenario, a user, when authenticated by a first domain, can access a client computer system associated with a second domain provided that a trust exists between the first and second domain. A group of mutually trusted domains is known as a “forest”. For example, a company may have a forest of domains, where each domain is associated with a particular group or organization (e.g., legal, human resources, accounting, etc.) within the company. Based on mutual trust between the domains of the forest, a user within the company can potentially log on to any client computer system within the company.
For the purposes of this discussion we refer to both forests and domains as ‘realms’. Note that even though the following descriptions refer to forests the concepts apply to other types of realms and collections of realms as well. The term domain controller refers to an instance of the realm. Many such domain controllers may be present in a realm. Situations exist in which one entity (e.g., company or organization) wants to grant access to computer resources within its forest to users from another entity. To accomplish this, a trust is established between a forest associated with the first entity and a forest associated with a second entity.
Users are granted access to a resource based on one or more sets of permissions associated with the resource and the user. Typically, a default set of permissions is granted to all users who are authenticated to access a particular resource. The default set of permissions provide an access level that is considered appropriate for any user that can authenticate to the resource. Within a single domain or resource, the default set of permissions that are granted to all users are typically those permissions that are appropriate for all members of the entity represented by the forest. However, when a trust is established between two forests, users from one forest may be allowed to authenticate to a resource in another forest, but the default access permissions that apply to all users of the resource may not be appropriate for a user that authenticates from a different forest. For example, it may be appropriate for users that authenticate within a single forest to have read access to a particular file resource, while it may not be appropriate for users that authenticate from a different forest to have any access to the particular file resource. This might be happen when the two forests are associated with different corporations or organizations. In other cases such as when the two forests are in the same organization it might make sense to have the same access permissions for users authenticated in either forest.
As such, it is important to be able to distinguish between access requests originating from users authenticated by a domain controller in a forest whose users can have the same set of permissions as users authenticated by a domain controller in the local forest versus requests originating from users authenticated by a domain controller in a forest whose users should not have the same set of permissions as users authenticated by a domain controller in the local forest. Other criteria may also be used to determine the type of request, such as whether the request originated from a realm associated with the same organization with which the requested resource is associated, or whether the request originated from one of a subset of users in the realm who are allowed to submit such a request.